After sneezing, we say, Alhamdulillah, and the people around are advised to say, Yarhamkumullah, God bless you. Would Huzoor kindly explain the significance and hikmah of these instructions? Sneezing has been investigated recently, in the recent age. While before this nobody knew the significance of sneezing and what is happening. In fact, there is a channel connecting the nasal passages with the brain. And there are fine ducts which are connecting the brain with these nasal passages.
Now, if some infection, some intruder particle, begins to travel towards the brain, then in between there are very sensitive filament-like things, mucous membranes, which are very highly sensitive. Now, they get irritated and you have the phenomena of sneezing. Then whatever was traveling upwards is with a very strong force ejected out and your life is saved. Otherwise, if this system had not been created by Allah, many a person would die because of brain infections or put into very great hardships and troubles.
So, this is why the one who sneezes says, Alhamdulillah, praise be to Allah for the creation of such protective system for me. And Yarhamkumullah is the answer of those who listen to him or observe this thing happen. They say, May Allah be always kind to you and show mercy to you.